The present invention relates to video interconnects with a cathode ray tube (CRT), and more particularly to a d.c. restore circuit for a multi-channel remote video interconnect to provide a d.c. restore function at each cathode or grid of a color CRT with minimum capacitance and without increasing the power of a video drive circuit.
Prior remote video interconnects, such as shown in U.S. Pat. No. 4,876,484 issued Oct. 24, 1989 to Roy O. Mitchell et al entitled "Remote Video Interconnect and Method", have a video driver that outputs a video signal to a transmission line. The transmission line couples the video signal to a cathode or grid of a cathode ray tube (CRT) to provide a suitable display of the video signal. For a monochrome system where only a single video channel is coupled to the CRT, a d.c. restore circuit is provided at the video driver in the form of a d.c. loop that samples the output current of the video driver. However, for a multi-channel system, such as a color CRT having a separate cathode or grid for each color component red, green and blue (RGB), each channel requires a different cutoff voltage at its respective cathode or grid. In order to provide these different cutoff voltages the video drivers have to be driven at different power levels. This results in a net increase in power of greater than three times that required for a single channel.
What is desired is a d.c. restore circuit for a multi-channel remote video interconnect that does not require increased power at the video driver while maintaining low capacitive loading to the cathodes or grids of a color CRT.